The present invention relates to a semiconductor device manufacturing method and, more particularly, to a semiconductor device manufacturing method in which the uniformity of patterning in the photolithography process (to be referred to as a PR process hereinafter) is improved and a semiconductor device fabricated by this method.
The prior art will be described with reference to FIGS. 6A and 6B, FIGS. 7A and 7B, and FIGS. 8A to 8D. As the prior art, a bolometer type infrared sensor described in Japanese Patent Laid-Open No. 80105794, in which bolometer type thermoelectric conversion elements are regularly formed, will be described, and a PR process for forming a bolometer will be particularly described. This prior art can be applied to a general semiconductor device in which required patterns are regularly formed in a predetermined region.
FIG. 6A shows the arrangement of a two-dimensional bolometer type infrared sensor. An infrared sensor 50 is constituted by a light-receiving portion 51, a horizontal scanner portion 52, a vertical scanner portion 53, and a signal output portion 54.
The light-receiving portion 51 is constituted by a large number of pixels 55 two-dimensionally regularly arranged in a matrix. The vertical scanner portion 53 sequentially selects pixel rows at a horizontal scanning time period so as to read all the pixel rows arranged in the light-receiving portion 51 in the vertical direction within a predetermined vertical scanning time. The horizontal scanner portion 52 selects pixel columns so as to sequentially read signals from the respective pixels 55 arranged in the horizontal direction in the respective pixel rows selected by the vertical scanner portion 53 within a predetermined horizontal scanning time.
The signal output portion 54 outputs the pixels 55 selected by the horizontal scanner portion 52 and vertical scanner portion 53. When the output terminal of the signal output portion 54 is connected to a unit that detects the resistance of the pixels 55, a change in resistance of the pixels 55 is detected, thereby detecting the two-dimensional information on the incident infrared ray. Reference numeral 59 denotes an outer peripheral portion where the horizontal scanner portion 52, the vertical scanner portion 53, and the signal output portion 54 are arranged.
FIG. 6B shows the pixel portion of the sensor shown in FIG. 6A. In each pixel 55, the temperature in the pixel 55 changes in accordance with the incident infrared ray, and the resistance of a bolometer 56 having a width al changes in accordance with this temperature change. This change in resistance is output from the corresponding pixel 55 to the outside as the signal through a pixel selection switch element (not shown) and interconnections 57 and 58 formed in the underlying substrate of the bolometer 56.
In the bolometer type infrared sensor having the above arrangement, the uniformity of the respective pixels 55 is significant. Accordingly, the resistance of the respective pixels 55 arranged two-dimensionally regularly, i.e., the uniformity of the resistance of the bolometers 56, is significant. To realize this uniformity, the interconnection width of the bolometers 56 in the light-receiving portion 51 must be uniformed.
FIG. 7A shows a photomask which is used in the conventional PR process for forming a bolometer and entirely covers the sensor. In this case, the photomask is used for the manufacture of the sensor shown in FIG. 6A. FIG. 7B shows a photomask portion shown in FIG. 7A which corresponds to one pixel portion.
Referring to FIG. 7A, a region 62 of a photomask 61 corresponds to the light-receiving portion 51. A region 63 of the photomask 61 is the surrounding region of the region 62, and corresponds to the outer peripheral portion 59. In the region 62, bolometer patterns 65 used in formation of the bolometers 56 of the light-receiving portion 51 are formed each with the predetermined width al to correspond to each pixel 55, as shown in FIG. 7B. Since the region 63 does not correspond to the light-receiving portion 51, it is made of a transparent material so that no patterns by the bolometer material layer are formed.
FIGS. 8A to 8D show a manufacturing method of forming the bolometers of the light-receiving portion. FIGS. 8A to 8D schematically show a section taken along the line A-A' of FIG. 6A and illustrate a case wherein the bolometers are formed by using the photomask 61 of FIG. 7A.
As shown in FIG. 8A, a bolometer material layer 202 serving as the material of the bolometers is deposited on an underlying substrate 201. As shown in FIG. 8B, a photoresist 203 is uniformly applied onto the bolometer material layer 202.
Subsequently, bolometer patterns 56 each shown in FIG. 7B is exposed within the light-receiving portion 51 (region 62) by using the photomask 61 of FIG. 7A, and is developed, to form bolometer patterns in the photoresist 203, as shown in FIG. 8C. At this time, on the outer peripheral portion 59 (region 63), the photoresist 203 is completely removed.
Using the photoresist 203 formed with the bolometer patterns as the mask, etching, e.g., plasma etching, is performed for the bolometer material layer 202 to form bolometers 206. At this time, on the outer peripheral portion 59 (region 63), the bolometer material layer 202 is completely etched and removed. Then, as shown in FIG. 8D, the photoresist 203 on the bolometers 206 is removed.
A bolometer 206b formed near the boundary of the light-receiving portion 51 is weakly developed and etched during the process of FIG. 8C to FIG. 8D. Accordingly, the bolometer 206b has a width a2 larger than the bolometer width al as the designed value on the photomask 61, and the pattern uniformity is degraded. The phenomenon wherein development and etching become weak near the boundary of the light-receiving portion 51 is called "microloading effect".
The "microloading effect" occurs when a wide region (region), e.g., the outer peripheral portion 59 (region 63), is removed around a region (pattern region), e.g., the light-receiving portion 51 (region 62), where regular patterns are formed, during formation of the bolometers. More specifically, in order to develop a photoresist or to etch a bolometer material layer over a wide region, larger amounts of developing agent, etching gas, and the like are used in the non-pattern region than in the pattern region. Accordingly, development and etching become relatively weak near the boundary of the non-pattern region, and a predetermined amount of development or etching is not performed. As a result, the width of the formed pattern becomes larger than the designed value of the photomask, and the pattern uniformity is degraded.
In FIG. 8D, only one bolometer 206b is wider than the predetermined width al. In fact, however, the width of the bolometers 206 gradually increases from the predetermined width al as it is closer to the boundary. In contrast to this, at a place remote from the boundary by a distance equal to or larger than a value to be described later, the width of the bolometers 206 is a predetermined value al, which is uniform.
As described above, since the width of the bolometer 206 of the pixel 55 located near the boundary between the light-receiving portion 51 and the outer peripheral portion 59 becomes larger than the predetermined value, the resistance of the bolometer 206 is decreased, and the uniformity of the resistance of the bolometers 206 in the light-receiving portion 51 is degraded.
In order to improve this pattern non-uniformity occurring near the boundary of the light-receiving portion 51, for example, Japanese Patent Laid-Open No. 63-17528 describes a method of forming regular dummy patterns also on the outer peripheral portion 59 of a predetermined region (pattern region) where regular patterns are formed.
The conventional method described above has problems as follows.
According to the first problem, when the dummy patterns are formed on the outer peripheral portion of the pattern region, an inconvenience such as degradation in characteristics of the semiconductor device occurs. This occurs when a different interconnection layer is formed under a layer where regular patterns are formed in the pattern region, not interposing an insulating protective layer. In other words, due to etching in the PR process of the dummy patterns, a specific portion of the underlying interconnection layer may become thin depending on the shape of the dummy patterns, to degrade the characteristics of the underlying interconnection layer or to short-circuit the underlying interconnection layer.
According to the second problem, when no dummy pattern is formed in order to avoid the first problem, the pattern width increases near the boundary of the pattern region, as described above, to degrade the uniformity. For example, in the bolometer type infrared sensor, the line width of the bolometer formed near the boundary of the light-receiving portion becomes larger than a predetermined value, and the uniformity of the resistance of the bolometers in the light-receiving portion is degraded.
The reason for this is as follows. As described above, during formation of the bolometers, when a wide region around the light-receiving portion is etched, the photoresist is developed weakly and the bolometer material layer is developed weakly near the boundary of the light-receiving portion (microloading effect), and a predetermined amount of etching is not performed.
When no dummy pattern is formed on the outer peripheral portion, due to the in-surface non-uniformity of the resistance, a sufficiently high gain cannot be obtained in a bolometer resistance detection circuit, and the S/N ratio of the detector does not increase.
This results from large variations in bolometer resistance near the boundary of the light-receiving portion as compared to a change in resistance of the bolometer in accordance with the incident infrared ray. When a signal including an offset component caused by the variations in resistance is to be set within the dynamic range of the detection circuit, the amplifier gain of the detection circuit is limited due to the variations in resistance. Accordingly, the amplifier gain cannot be increased when compared to a case free from variations in resistance. As a result, the signal component cannot be sufficiently increased, and the S/N ratio cannot be sufficiently improved against noise from the detection circuit and the like.
In order to cope with these problems, i.e., in order to increase the amplifier gain so as to obtain a high S/N ratio, if a circuit for correcting the variations in resistance is used, the size of the sensor circuit is increased, and the power consumption and the like are increased, leading to secondary problems.